Warfarin Dosing After 2 Days of 5 mg Daily
After giving 5 mg warfarin for 2 consecutive days, check the INR on day 3 before the next dose, then adjust based on the INR result: if INR <1.5, continue 5 mg daily; if INR 1.5-1.9, give 2.5-5 mg; if INR 2.0-3.0 (therapeutic), reduce to anticipated maintenance dose of 2.5-5 mg; if INR >3.0, hold the dose. 1
Initial Dosing Strategy
- The standard initial warfarin dose is 5 mg daily (or 2-4 mg in very elderly patients), avoiding loading doses that can cause excessive INR elevation 1
- With a 5 mg initial dose, the INR will not rise appreciably in the first 24 hours except in rare patients who ultimately require very small maintenance doses (0.5-2.0 mg daily) 1
- The steady-state anticoagulant effect is achieved in 5-7 days with the 4-5 mg/day initial dosing approach, which is also the anticipated maintenance dosage 2
Day 3 Management Algorithm
- Check INR on day 3 before administering the third dose, as this is when you begin to see the anticoagulant effect and can make informed adjustments 1, 3
- Monitor INR frequently (2-4 times per week) immediately after warfarin initiation, then gradually lengthen the interval up to a maximum of 4-6 weeks once INR values stabilize 1
Dosing Based on Day 3 INR:
- INR <1.5: Continue 5 mg daily, as the patient is responding normally and requires continued loading 1
- INR 1.5-1.9: Give 2.5-5 mg, as the patient is approaching therapeutic range 1
- INR 2.0-3.0 (therapeutic): Reduce to anticipated maintenance dose of 2.5-5 mg daily, as therapeutic range is achieved earlier than expected 1, 2
- INR >3.0: Hold the dose and recheck INR in 24 hours 1
Important Considerations
- Most warfarin dose adjustments should alter the total weekly dose by 5-20%, avoiding large dose swings that destabilize anticoagulation 1
- The dose does not need adjustment for a single INR slightly out of range if previously stable, though this principle applies more to maintenance therapy than initial dosing 4
- For rapid anticoagulant effect in emergent situations, heparin should be administered concurrently for 4-5 days due to the delay in factor II (prothrombin) suppression 3, 2
Common Pitfalls to Avoid
- Avoid loading doses (>5 mg initially) as they increase bleeding risk without improving time to therapeutic anticoagulation 1, 3
- Do not continue 5 mg blindly without checking INR on day 3, as some patients are highly sensitive and will become supratherapeutic 1
- Do not wait until day 5-7 to check the first INR, as this delays recognition of over-anticoagulation in sensitive patients 1
- In very elderly patients (>75-80 years), consider starting with 2-4 mg daily instead of 5 mg, as they have increased bleeding risk and often require lower maintenance doses 1, 5